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CVE-2026-21933: The Sandbox is Leaking: Deconstructing CVE-2026-21933 in Java Networking

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The Sandbox is Leaking: Deconstructing CVE-2026-21933 in Java Networking

Vulnerability ID: CVE-2026-21933
CVSS Score: 6.1
Published: 2026-01-20

CVE-2026-21933 is a deceptive 'Medium' severity vulnerability buried in the core Networking libraries of Oracle Java SE and GraalVM. Released in the January 2026 Critical Patch Update, this flaw allows unauthenticated remote attackers to bypass network restrictions via user interaction. While the CVSS score is a modest 6.1, the 'Scope Changed' (S:C) metric indicates that this vulnerability allows an attacker to pivot from the Java execution environment to affect the underlying host or other systems, effectively breaking the Java sandbox.

TL;DR

A logic flaw in Oracle Java's networking component allows attackers to bypass sandbox restrictions and potentially access internal network resources. Requires user interaction (e.g., clicking a link or running a Web Start app). Affects Java 8 through 25.

Technical Details

  • Attack Vector: Network (Remote, Client-Side)
  • CVSS v3.1: 6.1 (Medium)
  • Privileges Required: None (Unauthenticated)
  • User Interaction: Required (Click link/Run app)
  • Scope: Changed (S:C)
  • Exploit Status: None / Theoretical
  • Impact: Sandbox Escape / SSRF

Affected Systems

  • Oracle Java SE 8
  • Oracle Java SE 11
  • Oracle Java SE 17
  • Oracle Java SE 21
  • Oracle Java SE 25
  • Oracle GraalVM for JDK
  • Oracle GraalVM Enterprise Edition
  • Oracle Java SE: < 8u471 (Fixed in: 8u471)
  • Oracle Java SE: < 11.0.29 (Fixed in: 11.0.29)
  • Oracle Java SE: < 17.0.17 (Fixed in: 17.0.17)
  • Oracle GraalVM: < 21.0.9 (Fixed in: 21.0.9)

Mitigation Strategies

  • Update to the latest Java SE Critical Patch Update (January 2026)
  • Disable Java Web Start and Browser Applet plugins
  • Implement strict egress filtering on workstations
  • Use Endpoint Detection and Response (EDR) to monitor unexpected network connections from java.exe

Remediation Steps:

  1. Identify all installed instances of Oracle Java SE and GraalVM.
  2. Download the patches from the Oracle Technology Network.
  3. Install Java SE 8u471, 11.0.29, 17.0.17, 21.0.9, or 25.0.1.
  4. Restart any services or applications depending on the JDK.

References

Read the full report for CVE-2026-21933 on our website for more details including interactive diagrams and full exploit analysis.

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